1. Field of the Invention
This invention relates to an electrophotographic printing device, having a developer unit and a photoconductor, wherein the photoconductor is connected directly or with the interposition of one or several transfer media with a substrate to be imprinted, located in a transfer zone, wherein at least one charger is assigned to the substrate, and wherein the substrate can be conveyed through the transfer zone by a conveying device.
2. Discussion of Related Art
A printing device is known from German Patent Reference DE 198 49 500 A1. There, a developer unit is used, in which a toner is stored. A photoconductor drum is assigned to the developer unit. The photoconductor drum can be activated on its surface by an exposure device, so that a toner application becomes possible. The photoconductor drum is in contact with a transfer roller via a contact line. The toner is transferred from the photoconductor drum to the transfer roller using coronas. The transfer roller rolls off on the surface of a substrate which is to be imprinted. In the process the toner is transferred to the substrate surface using a corona arranged on the underside of the substrate. Two transfer processes of the toner image take place with this arrangement. The first transfer process occurs during the transfer from the photoconductor drum to the transfer roller, the second transfer process occurs during the transfer of the toner to the substrate. No complete transfer of the toner takes place during each of the transfer processes. However, the greatest possible transfer of the toner should be attempted, so that clear print images with sharp contours can be generated. In this connection the design and arrangement of the corona in the area of the second transfer process is of importance. It is necessary to assure that the surface of the substrate to be imprinted is sufficiently electrostatically charged. With flat substrates of greater wall thickness in particular, insufficient charging occurs when the substrate is of a material which does not conduct electricity well.